Cooling system for cutting tool and the like

ABSTRACT

A cutting tool cooling system including a cutting tool having an external cutting edge and an internal cavity with a heat receiving surface in heat exchange and fluid sealed relationship to the cutting edge, and a coolant in the cavity vaporizable at the cavity heat receiving surface for extracting heat therefrom and thereby cooling the tool cutting edge.

United States Patent Zerkle 1 May 23, 1972 [s41 COOLING SYSTEM FORCUTTING [s61 Rere neee cited TOOL AND THE LIKE UNITED STATES PATENTS[72] Inventor: Ronald D. Zerkle, Cincinnati, Ohio 1,129,925 3/1915Walser ..62/DIG. 10 1,820,073 8/1931 Kilbom ..165/ 1 X [73] Assgnee"Jemies Ohm a 3,465,813 9/1969 Bromberg et a1. 165/1 3,438,428 4/1969Balamuth et al.... 165/1 [22] Filed: Dec. 22, 1970 2,363,141 11/1944Pertics ...62/D1G. l0 A p No 100 589 3,376,918 4/1968 Foure etal..165/104X p Primary Examiner.lohn J. Camby Relmed Apphcauon DamAttorney-Wood, Herron & Evans [62] Division of Ser. No. 718,772, Apr. 4,1968, Pat, No.

3,571,877. [57] ABSTRACT A cutting tool cooling system including acutting tool having (g1. ..l65/1,62/D1G. an external cutting g and aninternal cavity with a heat [58] Fie'ld IDIG 10 receiving surface inheat exchange and fluid sealed relation- 62/295 6 ship to the cuttingedge, and a coolant in the cavity vaporizab1e at the cavity heatreceiving surface for extracting heat therefrom and thereby cooling thetool cutting edge.

2 Claims, 10 Drawing figures FATENTED MAY 2 3 1972 SHEET 3 BF 3 IllINVEUTOR. Mfi ZM BY COOLING SYSTEM FOR CUTTING TOOL AND THE LIKE removematerial from a workpiece such as a length of bar stock to alter itsshape, finish, and/or dimensions,-the workpiece is mounted in a machinefor motion relative to a cutting tool. The relative motion between theworkpiece and the cutting tool is effective to abrade, chip, shave, orotherwise cause removal of stock from the workpiece. Such relativecutting motion may be produced by movement of the workpiece relative toa substantially stationary cutting tool. Illustrative of such cuttingmotion is that which occurs in a turning lathe wherein the workpiece ismounted between centers-for rotation about its axis in cuttingrelationship to a tool whose cuttingedge contacts the workpieceperiphery. Alternatively, the'relative cutting motion may be establishedby movement of the tool relative to a substantially stationarilyheldworkpiece, such as occurs in a drilling machine wherein a drill bitrotatable about its axis is urged into the workpiece to afiect relativecutting motion.

Regardless of the manner in which the relative cutting motion isproduced, that is, by movement of the tool or workpiece or both, thecutting'process generates substantialheat. This heat is generated as aconsequence of two factors, namely, rubbing motion or friction betweenthe workpiece and the tool which occurs at the interface of theworkpiece and the tool cutting edge, and deformation of the materialconstituting the surface layer of the workpiece which occurs as chipsare formed. The amount of heat generated increases with increases inworkpiece hardness, tool cutting edge dullness, cutting edge andworkpiece relative velocity, and depth of cut. If the heat generated atthe tool-workpiece interface is not removed, the temperature of thetool, particularly the cutting edge, increases to a high value. As thoseskilled in the machine tool field will appreciate, high tool edgetemperatures are undesirable for a number of reasons. Principal amongthese is that hightemperatures increase tool wear. in fact, the amountof tool wear increases disproportionately fast with increasing tool edgetemperature. For example, according to one source, in the machining ofcertain materials tool wear varies directly with the temperature to thetwentieth power. This implies that a tool operating at l,500 F wearsnine times faster than a tool operating at l,300 F under the sameconditions. One of the most important consequences of increased toolwear is that it shortens tool life, and hence increases tool cost andmachine down-time.

Unduly high tool edge temperatures, in addition to increasing tool wear,also thermally damage the workpiece, reducing its strength anddeleteriously affecting its surface finish and appearance.

In the past, it has been proposed to reduce the temperature of the toolcutting edge by copiously applying liquid coolants to the externalsurface of the tool and workpiece. Typically, this has been accomplishedby directing a stream of liquid coolant, using a noule or the like,toward the tool-workpiece =interface. Theoretically, heat generated bythe cutting process at the tool-workpiece interface is conducted to theliquid,

which liquid is then transported away from the interface to efv fect atransfer of heat from the cutting edge and thereby reduce the cuttingedge temperature.

As those skilled in the art are aware, cooling of machine tool cuttingedges by the external application of liquid coolant has not beenentirely satisfactory for a number of reasons. Principal among these isthat external liquid cooling, at best, produces a low heat transfercoefficient, approximately l0-l00bL BTU/hour/square foot/degreeFahrenheit. This seriously limits the amount of heat that can be removedat a given stock removal rate for a given combination of tool andworkpiece, and hence the maximum attainable temperature reduction at thetool cutting edge. Additionally, external liquid cooling is not veryeffective above, temperatures of approximately 800 F, and attemperatures of '1 ,400 F and above is so ineffective that it isgenerally not used. A number of factors contribute to theineffectiveness of liquid cooling, particularly contamination ofthe'workpiece and environment. External liquid cooling has alsobeenknown to prevent oxidation of the chip, causing the chip to weld to thetool. This condition increases tool wear. It also increases the requiredcutting forces "by the amount necessary to shear the weldments andthereby permit further chip formation. Finally, external liquid coolingsubjects the tool to excessively large cyclic variations intemperatureas the tool undergoes cycles wherein it sequentially engagesthe workpiece to make a cutting pass therein and disengages theworkpiece'to enable tool repositioning for the successive cutting pass.The tool temperature rises during the cutting pass phase of the cyclewhen substantial heat is generated, whereafter it falls during the toolrepositioning phase when'no heat is generated, all during which time thetool may be continuously and uniformly subjected to a stream of coolant.These cyclic temperature variations cause the tool to be subjected toshock which in certain instances, such as when carbide tools are used,causes the tool to crack.

Certain disadvantages of the foregoing external liquid cooling proposalhave been obviated in the past by a second approach to the tool coolingproblem. In this approach, coolant in the form of vapor is introducedunder pressure of approximately-90 p.s.i. into a bore formed in thecutting tool. The vapor coolant is then forced from the bore throughorifices located behind the cutting edge which connect the bore with theatmosphere. Expansion of the vapor as it is released at the orificesabsorbs heat from the tool. This vapor coolant approach, because thevapor is much colder than the temperature of most liquid coolants,achieves higher rates of heat removal than frequently encountered withliquid cooling techniques. However, it has not removed all thedisadvantages of liquid cooling. For example, contamination of theenvironment is still a problem by reason of the escape of the vaporcoolant to the atmosphere. Additionally, complex apparatus in the formof evaporatols, pressure regulators, control valves and the like isrequired to provide the pressurized vapor necessary for this technique.

It has been an objective of this invention to provide a system forcooling cutting tools which is more effective than any heretofore known,particularly at high tool temperatures, and yet does not have the manydisadvantages accompanying prior art cooling techniques. This objectivehas been accomplished in accordance with certain principles of thisinvention by utilizing a fundamentally differentapproach to the designof a machine tool cooling system which represents a marked departure,both conceptually and in effectiveness, from the various cooling schemesheretofore proposed. Specifically, the foregoing objective has beenaccomplished by providing a unique, internal two phase tool coolingsystem which includes a cutting tool with an internal cavity'having aheat receiving surface in coolant sealed and heat exchange relationshipto the tool cutting edge, and coolant handling means for supplyingvaporizable coolant to, and removing vaporized coolant from, theinternal heat receiving surface of the cavity-With the above two-phasetool cooling system having the tool construction and coolant meansindicated, heat is very efficiently transferred from the cutting edge bythe coolant vaporization at the internal heat receiving surface and thesubsequent removal of the vaporized coolant to a remote point, toproduce reduction in tool edge temperature far greater than availablewith prior art proposals. I

In one form of this invention, the internal cavity is sealed andpreferably provided with capillary means, and the vaporizable coolant isliquid. The capillary means function to efficiently transport liquid tothe heat receiving surface from a heat transmitting surface of thecavity remote from the cutting edge. In accordance with this embodimentvaporizable liquid is transported to the heat receiving surfaceproximate the cutting edge by the capillary means where it is vaporized,extracting heat from the tool and thereby cooling the cutting edge. Thevaporized liquid is then caused to move, by reason of a pressuredifferential in the cavity, to the heat transmitting surface at the endof the cavity remote from the cutting edge where it condenses. The netresult of this process of liquid transport and subsequent vaporizationadjacent the cutting edge at the heat receiving surface, followed bycondensation of the vapor remotely at the heat transmitting surface, isthe production of a very efiicient, internal two-phase cooling methodfor reducing the temperature of a cutting tool.

In accordance with another embodiment of this invention the internalcavity of the cutting tool is provided with at least one opening forboth supplying liquid to the cavity and exhausting vapor therefrom.Preferably, in accordance with this embodiment, the cavity is providedwith two passages. One passage admits vaporizable liquid for subsequentvaporization at the internal heat receiving surface, while the otherexhausts vaporized liquid to the atmosphere, thereby enhancing thetransfer of heat from the cutting edge.

One of the principal advantages of this invention wherein internaltwo-phase cooling is utilized to cool the tool cutting edge is that heattransfer coefficients of l,00020,000 BTU/hour/square foot/degreeFahrenheit are possible. This is in contrast, for example, tocoefficients of from -1 ,000 BTU/hour/square foot/degree Fahrenheitattainable with presently proposed external fluid cooling techniques.Such heat transfer coefficients as are attainable with the coolingsystem of this invention result in substantial reductions in too] edgetemperature. For example, it has been found that at temperatures of 800F a temperature drop of 400 F is attainable in contrast to a temperaturedrop of 200 F attainable with conventional liquid cooling techniques.Since tool life increases markedly with decreased tool operatingtemperature, a drop of 400 F, while only representing a drop of twicethat attainable with conventional techniques, provides an increase intool life many times that obtainable using conventional liquid coolingsystems.

A further advantage of applicants invention attributable to the internalcooling aspect thereof is that contamination of the workpiece by thecoolant does not occur, nor does prevention of chip oxidation andsubsequent chip weldment to the tool present a problem. A further andequally important advantage of this invention is that conventionalmachine tools may be relatively easily structurally modified to operatein accordance with the principles of this invention. This eliminates theneed for costly tool changeovers. Additionally, very small quantities ofcoolant are required, and costly and complex coolant pumping apparatusis unnecessary. Also, a common coolant can be used for cutting differentmaterials, eliminating the need for stocking a variety of differentcoolants. Finally, it enables tool cooling to be used in hightemperature cutting operations, for example, above 1400 F, whereheretofore the available tool cooling was so ineffective that coolingwas not ordinarily used.

Other objectives and advantages of this invention will become morereadily apparent from a detailed description of this invention given inconjunction with the description of the drawings in which:

FIG. 1 is a perspective view of a preferred embodiment of a cutting toolutilizing certain of the machine tool cooling principles of thisinvention.

FIG. 2 is a plan view of a portion of the cutting tool depicted in FIG.1.

FIG. 3 is a cross sectional view taken along line 3-3 of FIG. 2.

FIGS. 4, 5, 6, 7 and 8 are views of additional embodiments of themachine tool cooling system of this invention.

Referring to FIGS. l-3, internal two-phase cooling of a cutting tool isdepicted in conjunction with an application in which the invention findsparticular, though not exclusive, utility. Specifically, it is depictedin conjunction with its use to cool a lathe turning tool. Referring toFIGS. l-3, a lathe turning tool 10 held by a tool post 12 is shown inoperative cutting relationship to a workpiece 14 mounted between centers18 and 20 for movement in the direction of arrow 16. The cutting tool10, considered in more detail, includes a shank or body 22 of generallyrectangular cross section having an inner end 24 and an outer end 26.The inner end 24 slideably interfits in an opening 28 formed in the toolpost 12 and having a cross section configured similarly, but slightlylarger than that of the cutting tool shank end. The cutting tool 10, byreason of the sliding fit between its inner end 24 and the opening 28 inwhich it is positioned, is adapted to be secured at selectively variablepositions along its longitudinal axis. To facilitate such securing, ascrew 30 threadable in the upper end of the tool post 12 is provided.The screw 30 when threaded down into the tool post, locks the cuttingtool in the axial position to which it has been inserted in the opening28.

The outer end 26 of the cutting tool 10 is provided with a triangularrecess 34 defined by vertical sides 34A and 34B and bottom 34C of shankend 26. A carbide insert 40 having a generally triangular cross-sectionof substantially the same configuration as the recess 34 is alsoprovided. The insert 40 has a cutting edge 48 defined by theintersection of a top surface 40A and a side surface 40B. The insert 40is adapted to be operatively positioned in the recess 34 and clampedtherein by a hold-down clamp 42. Clamp 42 has a lip which engages aportion of the upper surface 40A of the carbide insert 40 for securelylocking the insert in the recess 34 when a screw 44 passing through asuitable aperture in the clamp and threadably engageable with the endsegment 26 is tightened. When the insert is operatively positioned inthe recess 34, vertical insert side surfaces 40C and 40D intimatelycontact recess sides 34A and 34B, respectively, and the recess bottom34C intimately contacts the insert bottom 40E. Additionally, cuttingedge 48 extends beyond the side 38 of the shank end 26 The novel cuttingtool 10 of this invention depicted in FIGS. 1-3 further includes aninternal cavity or chamber 50. The cavity 50 includes a first, inner, orheat receiving surface region generally indicated by the referencenumeral 52 which is in heat exchange relationship with the cutting edge48 of the carbide insert 40, by reason of the intimate physical contactbetween the carbide insert and recess bottoms 40E and 34C, respectively.The heat receiving surface region 52 is also in fluid sealedrelationship to the cutting edge 48 of the tool 10 by reason of theinsert and tool material'separating the cutting edge and heat receivingsurface. The cavity 50 further includes a second, outer, or heattransmitting surface region 54 located more remote from the cutting edge48 than the heat receiving surface region 52. In practice the cavity 50may be formed by drilling a blind horizontal hole 56 from the verticaltool side 37 through the outer shank end 26 toward the opposite verticaltool side 38, in which case the heat transmitting surface 54 of thecavity 50 is opening in the shank end side 37 formed by the hole 56.Cooperating with the horizontal hole 56 is a vertical blind hole 58which intersects and thereby communicates with the hole 56. A plug 60inserted in the lower portion of the hole 58 seals the lower end of thevertical hole. The hole 58 may be blind as shown in FIG. 3, terminatingslightly below the interface of the recess and cavity bottoms 34C and40E, respectively. Alternatively, the hole 58 may be a through holecommunicating cavity 50 with the insert bottom 40E. In this case, theportion of the insert bottom 40E overlying the hole 58 combines with thesurface of the cavity 50 adjacent the overlying insert bottom surface toform the heat receiving surface 52. While the through hole embodimentenhances heat exchange between the cutting edge 48 and the heatreceiving surface 52, structural rigidity and strength of the tool 10may be slightly reduced.

Preferably positioned in the cavity 50 is a capillary means 62 whichextends the entire length of the cavity 50, having its inner end 62A incontact with the heat receiving surface 52 adjacent the bottom surface40E of the carbide insert 40 and its outer end 623 projecting from thecavity 50 in the vicinity of the heat transmitting cavity surface region54. The capillary means 62 preferably is fabricated of 120 meshstainless steel Dutch twill material configured in the form of a tube.

Associated with the cutting tool is a fluid means 70 for supplying fluidto the projecting end 62B of the capillary mesh 62. The fluid means 70is preferably in the form of a reservoir or trough secured to the outerend 26 of the tool shank 22. The trough 70 is provided with a suitablesupply of the fluid 72. The fluid 72 preferably is water provided with asuitable rust preventitive. The level of the water 72 is maintained bysuitable means, such as a dropper (not shown), above the extremity ofthe capillary means end 623.

In operation, liquid water 72 in the trough 70 is fed or pumped bycapillary action afforded by the mesh 62 from the trough along thehorizontal and vertical holes 56 and 58 to the heat receiving surfaceregion 52 of the cavity 50. Due to the relative motion at the interfaceof the cutting edge 48 of the carbide insert 40 and the workpiece l4,cutting edge 48 as well as contiguous and proximately located portionsof the insert 40 and the outer shank end 26, are heated to a level abovethe vaporization point of the water, causing vaporization of the waterpumped to the heat receiving surface region 52. The vaporized waterproduced at the heat receiving surface region 52, due to a pressuredifferential in the cavity 50, flows in the internal cavity 50 towardthe heat transmitting surface region 54 where it escapes to theatmosphere.

Continued supply of vaporizable liquid, such as water, from the trough70 to the heat receiving surface region 52 of the cavity 50 by thecapillary means 62, coupled with continued vaporization of the suppliedwater at the heat receiving sur face region, followed by exhaust to theatmosphere of the vaporized water via the outer end of the horizontalhole 56 located proximate the heat transmitting surface region 54,provides continued and highly efficient cooling of the cutting edge 48of the carbide insert 40. The efficiency of the cooling process isattributable to the extremely high heat transfer coefficients affordedby the vaporization of the liquid occurring at the heat receivingsurface region 52 of the cavity 50. In practice heat transfercoefficients of LOGO-5,000 BTU/hour/square foot/degree Fahrenheit arepossible with the tool cooling apparatus of this invention. This heattransfer coefficient is in contrast, for example, to rates of .101,000BTU/hour/square foot/degree Fahrenheit achievable with conventionalliquid cooling techniques.

As those skilled in the art will appreciate, numerous modifications inthe preferred embodiment depicted in FIGS. l-3 may be provided withoutdeparting from the spirit and scope of this invention. For example,while the preferred embodiment has been provided with capillary means 62to supply vaporizable fluid to the inner surface region 52 of the cavity50 such capillary means are only preferred, and may be omitted ifdesired. If the capillary means 62 are omitted, the vaporizable fluidmay be supplied to the inner surface region 52 of the cavity 50 bygravity feed or fluid pressure means.

Where capillary means are utilized the capillary means may take manyforms. For example, the capillary means 62, while disclosed as being 120mesh stainless steel Dutch twill and having a tubular cross section, maybe fabricated of other materials having different cross-sections. Forexample, other porous capillary means, such as woven cloth or fabricwicks, having other mesh sizes may be used. Additionally, thecrosssection of the capillary means may be V-shaped, oval, flat or thelike. If the cross-section of the capillary means is V- shaped, thecapillary means itself functions as a trough or conduit for supplyingvaporizable fluid to the heat receiving surface region 52 of the cavity50. Capillary material, if used, should be selected to be noncorrosivewith respect to the vaporizable fluid 72. Additionally, the capillarymeans 62 when inserted in the cavity 50 must not have a bulk or volumesuch that the internal cavity becomes constricted, thereby unnecessarilyimpeding the escape or exhaust of vaporized fluid to the atmosphere. Ifthe internal cavity 50 becomes unnecessarily constricted by reason of anexcess volume of capillary means therein, the escape of vaporized fluid,and hence the heat transfer efficiency of the system, is reduced.

The cavity 50 need not have a circular cross-section nor be comprised ofintersecting horizontal and vertical bores. The internal cavity 50 maybe formed in a variety of configurations and shapes to suit the needs ofthe user. In designing the shape of the internal cavity 50, to obtainoptimum results, the cavity should have a heat receiving surface region52 which is as large and as close to the cutting edge 48 as possibleconsistent with obtaining a structure which prevents film boiling of thevaporizable fluid and is sufficiently. strong to withstand the stressand forces encountered in the cutting process.

The vaporizable fluid 72 may be comprised of a variety of differentmaterials or combinations thereof. For example, while water has beenfound to be preferable for cooling tools with cutting edge temperaturesas high as 1400F, other vaporizable fluids may be used. For example,organic liquids such as ethyl and methyl alcohol, and fluorocarbons suchas freon are suitable substitutes. If desired, the vaporizable fluid maybe refrigerated to enhance the heat transfer process. In the selectionof the vaporizable fluid it is only necessary that the fluid bevaporizable at the temperature to which the heat receiving surfaceregion 52 becomes elevated by reason of the heat generated by thecutting process and conducted to the heat receiving surface. Preferably,however, the vaporizable fluid should have a highlatent heat ofevaporation, and a high surface tension.

Another embodiment of the tool cooling system of this invention isdepicted in FIG. 4. Referring to FIG. 4, a lathe cutting tool is shownin longitudinal cross-section. The tool 80 includes a shank 84 having anouter end 82 provided with a cutting edge 86 in cutting relationship toa moving workpiece 83, and an inner end 88 secured to a tool post 90 bymeans of a cooperating screw 92. The tool 80 is provided with aninternal cavity 94 having a first or heat receiving surface region 96 inheat exchange and fluid sealed relationship to the cutting edge 86, anda second or heat transmitting surface region 98 spaced more remote fromthe cutting edge 86 than the surface region 96. The cavity 94 is shownschematically and may be formed by a variety of machining processes wellknown by those skilled in the art and therefore not discussed in detailherein. Preferably, the heat receiving surface 96 is spaced as close tothe outer surface region 87 proximate the cutting edge 86 as possibleconsistent with tool strength and ability to withstand forces present inthe cutting process.

A suitable capillary means 100, such as a mesh material, lines theinternal surface of the cavity 94, being in intimate contact with thesurfaces 96 and 98. The mesh material 100 functions to supply avaporizable fluid 102 to the heat receiving surface 96 from a poolformed in the vicinity of the heat transmitting surface 98.

In operation, the heat generated at the outer end of the cutting tool 80by the cutting process, particularly at the cutting edge 86, isconducted through the cutting tool outer end 82 to the heat receivingsurface 96 of the cavity 94. At the heat receiving surface 96, thevaporizable fluid supplied by the mesh 100 from the pool 102 at the heattransmitting surface 98 is vaporized, extracting heat from the outer end82 of the tool 80. The vaporized fluid is then transported, by reason ofa pressure differential in the cavity 94 to the opposite end of thecavity where it condenses on the heat transmitting surface 98 which ismaintained at a temperature below the condensation The vaporizablefluid, following condensation at the heat transmitting surface 98,enters the pool 102 wherein it is subsequently transported by capillaryaction of the mesh 100 back to the heat receiving surface 96 of thecavity 94 whereupon the cycle of vaporization, vapor transport,condensation, and vaporizable fluid transport is repeated, providing acontinuous transfer of heat at high efficiency from the tool cuttingedge 86 to the coolant 106. The transfer of heat from the tool cuttingedge 86 may be enhanced by using, as the vaporizable fluid, liquidmetals suchas liquid sodium, liquid lithium, or other suitable liquidmetals having high specific heats.

FIGS. 5, 6, 7A and 7B, and 8A and 8B depict four further embodiments ofthis invention. In FIGS. 5, 6, 7A and 7B, and 8A and 83 referencenumerals identical to those appearing in FIG. 4 are utilized to indicatestructural elements in these Figures which find substantially identicalcounterparts in FIG. 4. The modifications of the tool of FIG. 4, whichare depicted in FIGS. 5, 6, 7A and 7B, and 8A and 8B provide two-phaseinternal cooling systems which may be classified as open systems incontrast to the closed two-phase internal cooling system of FIG. 4.Specifically, in FIG. 5 a passage 120 communicating at one end with thesurface 108 of the inner tool end 88 and at the other end with the heattransmitting surface region 98 of the cavity 94 is provided. The passage120 permits vaporizable fluid which has been vaporized at the heatreceiving surface 96 to exhaust to the atmosphere, as well as permitsinsertion of a conduit 122 for supplying vaporizable fluid from a source(not shown) to the interior of the cavity 94 for subsequent vaporizationat the heat receiving surface 96.

The structure of FIG. 6 includes, in addition to the passage 120, asecond passage 130. The passage 130 at its lower end communicates withthe cavity 94 at a point proximate the heat receiving surface 96 and atits other end with the atmosphere. To prevent constriction of the vaporoutlet passage 130 by accumulated chips, a suitable vapor chip shield(not shown) can be provided. Alternatively, the passage 130 may belocated in the vertical side wall of the cavity. In the embodiment ofFIG. 6 vaporizable fluid is admitted to the cavity 94 through thepassage 120, and provides a supply of vaporizable fluid to the heatreceiving surface 96. Vaporized fluid generated at the heat receivingsurface 96 exhausts through the passage 130 to the atmosphere. Byexhausting the vaporized fluid at a point adjacent the heat receivingsurface 96, pre-heating of the vaporizable fluid as it moves toward theheat receiving surface 96 from the inlet passage 120 is reduced to aminimum.

In the embodiment of FIGS. 7A and 7B the cavity 94 of the tool 80 isprovided with an opening 140 in the end 88 which communicates, via atube 141 connected to and extending therefrom, with a fluid supply hose142. Also included is an opening 144 communicating at one end with thecavity 94 adjacent the outer shank end 82, and communicating at theother end with the atmosphere. The passage 144 intersects the interiorof the cavity 94 at a point approximately midway between the'bottomcavity surface 145 and the top cavity surface 146.

In operation, fluid is admitted into the cavity 94 by the hose 142 andtube 141 where it is pressure fed to the capillary means 100 and thenceto the heat receiving surface 150 of the cavity by the capillary means100. At the heat receiving surface 150, the vaporizable fluid isvaporized by the heat transported thereto from the cutting edge 86,lowering the cutting edge temperature. The vaporized fluid then exhauststo the atmosphere via the passage 144.

The passage 144, in addition to serving as an exhaust for the vaporizedfluid, also acts as an overflow for unvaporized fluid fed to the cavity94 by the hose 142. In practice, fluid flow from the hose 142 isregulated to rate where there is a very slight trickle of unvaporizedfluid from the passage 144. The presence of such a trickle provides anindication that a sufficient and proper supply of vaporizable fluid isbeing fed to the capillary means 100 for subsequent transport to theheat receiving surface 150.

The embodiment of FIGS. 8A and 8B includes a cutting tool having aninner end 88 securable to a tool post (not shown), and an outer end 82provided with a recess 166 in an upper comer thereof functioning in amanner similar to recess 34 of FIGS. 1-3. Positioned in the recess 166is a carbide insert 168 having a cutting edge 86 which serves a functionsimilar to that of the carbide insert 40 of FIGS. l-3. Positioned abovethe carbide insert 168 is a chip breaker 170. Both the chip breaker 170and the carbide insert 168 are stationarily secured in the recess 166 bya suitable clamp 172.

The outer end 82 of the tool 80 is provided with an internal cavity 94having a heat receiving surface comprising the bottom surface of thecarbide insert 168, and a heat transmitting surface including an opening176 connecting the cavity 94 and atmosphere. The opening 176 ispositioned approximately midway between the bottom and top of the cavity94. The cavity 94 is provided with an opening 178 connecting the cavityand one end of a tube 179 secured to the tool end 82. The other end 180of the tube 179 is open to the atmosphere. Inserted in the tube 179 andthe cavity 94 is a tubular capillary means 100 which extends between theheat receiving surface 175 at one end of the cavity and a point beyondthe opening 180 ofthe tube 179.

In operation, vaporizable fluid is gravity fed to the capillary means100 from a dropper positioned above the projecting capillary means end182. The gravity fed fluid is thereafter transported by the capillarymeans 100 to the heat receiving surface 175 of the cavity 94. At theheat receiving surface 175, the vaporizable fluid is vaporized by theheat transmitted thereto from the cutting edge 86 of the carbide insert168. The vaporized fluid then exhausts from the cavity 94 to theatmosphere via the passage 176.

The function and operation of the passage 176, in addition to serving asan exhaust for the vaporized fluid, also serves as an overflow for theunvaporized fluid fed to the cavity 94 from the dropper 185 via thecapillary means 100. In practice, the rate of emission of fluid from thedropper 185 is regulated to just provide a trickle of vaporizable fluidoverflowing through the passage 176. This trickle provides an indicationthat a sufficient and proper supply of vaporizable fluid is being fed tothe heat receiving surface 175 of the cavity 94.

The vaporizable liquid utilized in the embodiments of FIGS. 5, 6, 7A and7B, and 8A and 8B, like the vaporizable fluid utilized in theembodiments of FIGS. l-3, preferably is water, although as indicatedpreviously other fluids may be employed. The vaporizable fluid utilizedin the embodiment of FIG. 4 preferably is a liquid metal, such as liquidsodium, potassium, etc. Water is not preferred due to the high pressuresdeveloped when utilized in a closed system of the type depicted in FIG.4.

The invention has, for the purpose of clarity and illustration, beendisclosed with reference to its use in a system for cooling cuttingtools of the type used in turning lathes. However, those skilled in theart will readily understand that the invention is susceptible of use forcooling other types of cutting tools. For example, it is contemplatedthat this invention can be used to cool drill bits, milling cutters, andthe like. It also is contemplated that this invention may be used tocool forming tools, such as punches and dies.

Having described the invention, what is claimed is:

1. A method of cooling a machine tool having an external cutting edgeand an open internal chamber with a heat-receiving surface thereof inheat exchange relation to the cutting edge, comprising the step of:

supplying by capillary action substantially unpressurized liquid coolantto said heat-receiving surface for vaporization thereat, without filmboiling, by heat transmitted thereto from said cutting edge.

2. The method of claim 1 comprising the further step of exhaustingvaporized liquid coolant from said chamber to atmosphere via a vaporexhaust passage in said tool which communicates with the atmosphere andwith the interior of said chamber proximate said heat-receiving surface.

1. A method of cooling a machine tool having an external cutting edgeand an open internal chamber with a heat-receiving surface thereof inheat exchange relation to the cutting edge, comprising the step of:supplying by capillary action substantially unpressurized liquid coolantto said heat-receiving surface for vaporization thereat, without filmboiling, by heat transmitted thereto from said cutting edge.
 2. Themethod of claim 1 comprising the further step of exhausting vaporizedliquid coolant from said chamber to atmosphere via a vapor exhaustpassage in said tool which communicates with the atmosphere and with theinterior of said chamber proximate said heat-receiving surface.